Are marine planktonic invertebrates food limited? The case of Mysis mixta (Crustacea,Mysidacea) in the Baltic Sea

Summary Linear regression analysis of field data from a coastal area of the Baltic Sea indicated that growth of the zooplanktivorous Mysis mixta was food limited. No statistically significant effects of temperature on growth were detected.     

Werner Schnese and the Development of Coastal Waters Ecology in Rostock,GDR

A survey of ecosystem research in brackish coastal waters (Baltic Sea) by the Department of Biology, University Rostock (GDR) is given. Using selected results the main goals are demonstrated, outgoing from the first steps initiated by W. Schnese.     

Influence of Eutrophication on the Distribution of Phytobenthic Plant and Animal Communities

A short review of effects of eutrophication on the phytobenthic communities in the Baltic Sea is given. Future monitoring aspects are briefly discussed. Local changes in phytobenthic communities outside point sources (e.g. industry outlets, enclosed bays receiving effluents from land runoff etc.) are easily detected and can be due to nutrient enrichment and/or toxic substances. In recent decades, changes have been reported from apparently unaffected areas. The disappearance of Fucus vesiculosus is the most conspicuous. The cause of events is similar in those areas: increases in epiphytes give increases in grazer populations. The thallus of algae is heavily grazed upon. The epiphytes shade their host and filamentous algae compete for space, disturbing recruitment and leading to a decrease in diversity. The rapid response of opportunistic filamentous algae on nutrient enrichment and changing herbivore pressure can easily be observed. Therefore, repeated surveillance in defined areas, which integrates the environmental response in both animal and plant communities, may be a fruitful approach for detecting large scale eutrophication of the Baltic Sea.     

中华鲟人工繁殖放流现状评价

1984-1998年,在长江葛洲坝水利枢纽下游江段,中国集团公司中华鲟研究所共捕捞663尾中华鲟亲鱼用于人工繁殖。各年的捕捞量变动在31—60尾之间。实际用于人工催产的亲鱼年利用率变动在3.1—91.7％之间。平均28.4％。催产卵的年受精率变动在0—85.0％之间,平均66.5％。年人工孵化鲟苗量变动在5—151.9万尾之间,平均54.3万尾。历年合计向长江放流初孵鲟苗4258万尾、幼鲟6.28万尾。经过多年的实践,中华鲟的人工催产,幼鲟孵化、培育和放流等方面的技术已经发展成熟。     

Analysis of motility parameters from paddlefish and shovelnose sturgeon spermatozoa

Ninety to 100% of paddlefish Polyodon spathula were motile just after transfer into distilled water, with a velocity of 175 μm s^-1, a flagellar beat frequency of 50 Hz and motility lasting 4–6 min. Similarly, 80–95% of shovelnose sturgeon Scaphirhynchus platorynchus spermatozoa were motile immediately when diluted in distilled water, with a velocity of 200 μm s^-1, a flagellar beat frequency of 48 Hz and a period of motility of 2–3 min. In both species, after sperm dilution in a swimming solution composed of 20 mM Tris–HCl (pH 8·2) and 20 mM NaCl, a majority of the samples showed 100% motility of spermatozoa with flagella beat frequency of 50 Hz within the 5 s following activation and a higher velocity than in distilled water. In such a swimming medium, the time of motility was prolonged up to 9 min for paddlefish and 5 min for sturgeon and a lower proportion of sperm cells had damage such as blebs of the flagellar membrane or curling of the flagellar tip, compared with those in distilled water. The shape of the flagellar waves changed during the motility phase, mostly through a restriction at the part of the flagellum most proximal to the head. A rotational movement of whole cells was observed for spermatozoa of both species. There were significant differences in velocity of spermatozoa between swimming media and distilled water and between paddlefish and shovelnose sturgeon.     

Nitrogen fixation by Baltic cyanobacteria is adapted to the prevailing photon flux density

N₂ fixation, measured as acetylene reduction, was studied in laboratory cultures and in natural assemblages (both as a mixed population and as individually picked colonies) of the heterocystous cyanobacteria Aphanizomenon sp. and Nodularia spp. from the Baltic Sea. During a diurnal cycle of alternating light and darkness, these organisms reduced acetylene predominantly during the period of illumination, although considerable activity was also observed during the dark period. In both laboratory cultures and natural populations N₂ fixation was saturated below a photon flux density of 600 μm⁻² s⁻¹. In cyanobacterial blooms in the Baltic Sea, nitrogenase activity was mostly confined to the surface layers. Samples collected from greater depths did not possess the same capacity for acetylene reduction as samples from the surface itself, even when incubated at the photon flux density prevailing in surface waters. This suggests that, with respect to N₂ fixation, Baltic cyanobacteria are adapted to the intensity of illumination that they are currently experiencing.     

Non-native Species and Rates of Spread: Lessons from the Brackish Baltic Sea

The Baltic Sea, a semi-enclosed brackish water region, has been inoculated by non-indigenous species for centuries. Today, much of its biological diversity is of foreign origin (i.e. xenodiversity), intentionally or unintentionally moved by humans over ecological and geographical barriers. As many as 98 introduced species have been recorded in the Baltic Sea and Kattegat. The role and abundance of much of the unique native brackish water fauna of the Baltic Sea are threatened by these non-indigenous species. The rate of primary introductions into the Baltic has increased since the 1950s; the secondary rate of spread of non-indigenous species within the basin varies from 30–480 km/year. We review here the invasion histories of the brown alga Sargassum muticum (introduced in the early 1990s), the mud snail Potamopyrgus antipodarum (1887), the barnacle Balanus improvisus (1844), the polychaetes Marenzelleria viridis (1985) and Polydora redeki (1963), the cladoceran Cercopagis pengoi (1992) and the mysid shrimp Hemimysis anomala (1962). This revised version was published online in July 2006 with corrections to the Cover Date.     

Control of macroalgal blooms at early developmental stages: Pilayella littoralis versus Enteromorpha spp.

Although blooms of opportunistic fast-growing macroalgae now occur frequently in coastal ecosystems affected by eutrophication, their initiation and control is little understood. Most previous studies have focused on the ecophysiology of adult algae only. We show that spores and/or germlings may represent critical stages in the life cycles and mass-developments of co-occurring opportunistic macroalgae in the Baltic (Pilayella littoralis and Enteromorpha spp.). We investigated the overwintering of spores, timing of germination, subsequent growth, and grazing on spores and germlings, in order to explain the initiation of mass blooms and species dominance patterns. In the field, Enteromorpha spp. showed 10- to 50-fold higher abundances of overwintering microscopic forms (up to 330 individuals cm⁻²) than P. littoralis. Moreover, we found continuous production of spores (up to 1.2 million settling spores m⁻² h⁻¹) from April to October in Enteromorpha spp., while there was evidence of only a short reproductive period in Pilayella. However, in spring, germlings and adults of P. littoralis appeared earlier in the field and reached a 10-fold higher biomass than Enteromorpha spp. In factorial laboratory experiments including temperature and light, there were clear differences in timing of germination. P. littoralis germinated at 5°C whereas Enteromorpha spp. required temperatures of 10–15°C for germination. In contrast, we detected only minor differences in growth response among adults of P. littoralis and Enteromorpha spp. Germination, not growth of adults, appeared to be the ecophysiological bottleneck for initiating mass spring development. Following the spring Pilayella bloom, Enteromorpha germlings occurred massively in the field (April–September), but rarely developed into adults. In laboratory feeding experiments we tested whether crustacean mesograzers common in summer may control development of Enteromorpha germlings. Both germination of settled spores and growth of germlings were reduced by 93–99% in the presence of grazers (Idotea chelipes and Gammarus locusta). Thus in addition to ecophysiological constraints, grazers, if present, may play a decisive role in the early life stages of macroalgal mass developments. These results mirror patterns of overwintering of seeds, germination control, seed and seedling predation in terrestrial plant communities. Received: 7 March 1998 / Accepted: 18 November 1998     

Genetic distinction of pallid, shovelnose, and Alabama sturgeon: emerging species and the US Endangered Species Act

The sturgeon genus Scaphirhynchus consists of threerecognized species. Pallid and shovelnose sturgeon (S. albusand S. platorynchus, respectively) are sympatric in theMissouri and lower Mississippi Rivers of the central United States. TheAlabama sturgeon (S. suttkusi) is endemic to the nearby MobileRiver drainage and is isolated geographically from the other twospecies. Pallid sturgeon and the extremely rare Alabama sturgeon arelisted as endangered under the US Endangered Species Act (ESA).In contrast, shovelnose sturgeon are relatively common and are notlisted. Despite these taxonomies and morphological evidence, somebiologists have questioned the genetic and taxonomic distinctions of thethree species, thus raising doubts concerning the validity of protectingpallid and Alabama sturgeon under the ESA. To investigate thesequestions, we compared a 436 base-pair sequence of the mitochondrial DNA(mtDNA) control region among the three species. We observed 16 mtDNAhaplotypes defined by 27 single base-pair substitutions (transitions)and one single base-pair insertion/deletion (indel) among 78individuals examined. The maximum sequence divergence among thosehaplotypes (2.06%) was less than values usually observed betweenfish species. However, Alabama sturgeon (n = 3) weredistinguished from the other two taxa (n = 75) by aunique base-pair substitution and haplotype, and pallid and shovelnosesturgeon at their northern range of natural sympatry (upper MissouriRiver) did not share any haplotypes. On the other hand, only frequencydifferences among shared haplotypes distinguished (P < 0.01)pallid and shovelnose sturgeon at their southern range of naturalsympatry (Atchafalaya River), and genetic distances between northern andsouthern localities for each species were nearly as large as thedistances between species. These latter results are consistent withseveral hypotheses, including reports (based on morphology) of putativenatural hybrids in the Atchafalaya River but not in the upper MissouriRiver. Overall, these mtDNA results indicate significant reproductiveisolation between pallid and shovelnose sturgeon in areas of naturalsympatry, and recent evolutionary divergence of Alabama sturgeon. ThesemtDNA results provide the first molecular genetic evidence fordistinguishing the three Scaphirhynchus species and, coupledwith morphological and biogeographic data, indicate that pallid andAlabama sturgeon should be evaluated as distinct species under theESA.